A boiler is sometimes provided for a large steam turbine which can only be started with a turbine bypass system. When starting a cold turbine, however, the turbine is required to be rolled after insufficient time for warming of the rotors on turning gear. Low pressure turbine bypass valves control reheat steam pressure to the reheat turbine. If the turbine is rolled with a cold HP rotor, however, water will condense and accumulate in the HP rotor, possibly leading to erosion of the HP buckets at speeds greater than approximately 1000 rpm, if insufficient flow through the HP turbine section does not blow out any freshly forming condensate. If insufficient steam flows through the low pressure turbine section, overheating of the last stages of the LP turbine section will occur at higher speed.
A problem exists in that with the reheat pressure controlled by the low pressure bypass valves, two sets of controlling turbine valves must be used to control a single turbine speed, i.e., stop/control valves controlling steam to the HP turbine section, and reheat stop/intercept valves controlling steam to the reheat or IP turbine section as well as the LP turbine section. It is normal that slight miscalibration of the controlling valves will exist, which can lead to either starving of flow in the HP turbine section or LP turbine section, resulting in erosion in the HP turbine section and/or overheating in the LP turbine section.